Method of and apparatus for effecting superior sanding

ABSTRACT

A sanding machine with complementary upper and lower sanding heads which have fast moving abrasive belts trained about and constantly shifted edgewise along superimposed contact drums between which the work is fed in a manner whereby the parallel narrow zones of work performing engagement of the abrasive belts with the opposite sides of the work extend at an oblique angle of not more than 75* to the lengthwise dimension of the work.

United States Patent Sternal [151 3,654,738 1 Apr. 11, 1972 [54] METHODOF AND APPARATUS FOR EFFECTING SUPERIOR SANDING [72] Inventor: LambertS. Sternal, Wayzata, Minn.

[73] Assignee: Timesavers Sanders, Inc., Minneapolis,

Minn.

[22] Filed: Sept.ll, 1970 [21] Appl.No.: 71,546

Related US. Application Data [63] Continuation-in-part of Ser. No.860,860. Sept. 25.

1969, abandoned.

[52] U.S.Cl ..5l/l39,51/141 [51] Int. Cl ..B24b 21/00 [58] FieldofSearch.... ..5l/135-147; 144/117 A, 2 R

[56] References Cited UNITED STATES PATENTS 2,762,173 9/1956 Bootcher..5 H141 FOREIGN PATENTS OR APPLICATIONS 49,730 11/1889 Germany 144/2 RPrimary Examiner-Othell M. Simpson Attorney-Ira Milton Jones [57]ABSTRACT A sanding machine with complementary upper and lower sandingheads which have fast moving abrasive belts trained about and constantlyshifted edgewise along superimposed contact drums between which the workis fed in a manner whereby the parallel narrow zones of work performingengagement of the abrasive belts with the opposite sides of the workextend at an oblique angle of not more than 75 to the lengthwisedimension of the work.

8 Claims, 5 Drawing Figures PATENTEUAPR H I972 3, 654, 738

sum 3 BF 4 METHOD OF AND APPARATUS FOR EFFECTING SUPERIOR SANDING Thisinvention like that of the copending application Ser. No. 860,860 filedSept. 25, 1969, now abandoned of which this is a continuation in part,relates to sanding machines, and especially to belt sanders designed tosize and finish roughsawn boards and lumber. Such machines havecomplementary upper and lower sanding heads between which the work isfed so that in one pass through the machine both sides of the work aresanded.

The purpose and object of the invention is to make possible the sizingof rough-sawn lumber on a belt sander at production rates far in excessof those heretofore considered feasible. Prior to this invention, no onewould consider feeding lumber through a belt sander at more than 250feet per minute. With this invention, rough-sawn lumber can be fedthrough the sander at 800 feet per minute, which is approximately therate lumber is fed through a conventional rotary knife planer.

But if a planer is used for sizing lumber, considerable waste isinevitable. It is not possible to take a light cut with a planer withoutburning the knives. Hence the rough sawn stock must be cut considerablylarger than the desired final dimensions to enable the lumber to bedressed to size with a planer.

A belt sander, on the other hand, can take off as light a cut as desiredand, with the sanding belts now available, can also remove considerablestock in a single pass; and in each instance will produce a smoothersurface than that obtained with a planer. To be specific, with the beltsander of this invention, 0.050 of an inch 0.025 per side is removed at800 feet per minute.

In view of the greatly increased feed rate made possible by thisinvention, there is no longer any plausible reason for not sizing roughsawn lumber with a belt sander. On the contrary, there is a mostimpelling reason for doing so a better product at lower cost.

Not only has this invention achieved phenomenally increased feed rates,but it has also eliminated the objectional characteristic of sandedsurfaces known as grain relief, which consists of low and high areas inthe finished surface, generally following the grain, and which wasencountered when certain species of wood were processed withconventional sanding machines, an example of which is disclosed in theNylund US. Pat. No. 3,269,065.

Those skilled in this art know that in belt sanders, as in drum sanders,the heavy work performing engagement between the abrasive surface andthe workpiece is confined to a narrow zone which extends transverselyacross the path of the workpiece as it moves through the machine.Ordinarily, this narrow zone of action extends squarely across, ornormal to the path along which the conveying means of the machineadvances the work. Hence when boards, planks, panels or other woodensurfaced workpieces are fed through the machine in the conventional way,with the lengthwise dimension thereof parallel to the path of travel,the sanding is done with the grain.

It has been found that when some species of wood are processed in thisconventional way, at high feed rates and heavy sanding pressure insanding machines of the type represented by the aforesaid Nylund patent,considerable grain relief resulted that is, the surfaces had pronouncedhigh and low areas generally following the grain of the wood. Douglasfir was especially susceptible to this objection.

While the reason for this lack of uniformity or deviation from trueflatness is not fully understood, it is believed that it is caused bythe compressibility of the abrasive belts. It has been observed thatwhen these belts are new, they cut the softer grain more aggressivelythan the harder grain. This results in a low spot wherever the softergrain exists; but when the belt has been in use for an appreciable timeand its abrasive surface becomes loaded with wood dust so that it doesnot cut as well, the reverse is true. Such a loaded belt has lost someof its compressibility and because it does not cut freely, it has atendency to compress the softer areas of the wood surface being sanded.Hence when these areas are relieved of compression they relax and riseabove adjacent harder grain areas.

It is realized that the theory just expressed does not comport with thecontention made in the aforesaid Nylund US. Pat. No. 3,269,065, in whichthe following statement is made at column 9, lines 54-60:

Hard, relatively unelastic spots distributed over the faces of the panelare subjected to the major sanding action. Soft, more elastic portionsare sanded with lighter pressure. Any tendency for these soft, moreelastic portions to be gouged out below the plane of the hard portions,as noted in usual sanding operations, is eliminated.

Whatever the answer to this disparity in theory might be, actual testswith a simultaneous top and bottom sander similar to that of the Nylundpatent, using 36 grit belts running at 6,300 sfpm and a work feed rateof fpm, and loading the machine in the conventional manner with four 6inch wide planks of Douglas fir and removing 0.025 inch per side,objectionable grain relief was encountered.

It was then discovered that the objectionable lack of surface flatnesswas overcome by having the boards fed through the machine with theirlongitudinal edges which are generally parallel to the grain disposed atan angle of at least 15 to the path along which they were carried to andthrough the machine. Apparently the resulting partially cross-grain sanding prevented what had caused the objectionable grain relief, for it wasfound that whether the belt was new and cutting aggressively, or loadedand compressing the softer grain, a superior and far more level surfacewas obtained.

If the boards were placed at an angle to the path along which they movedwhich was substantially less than 15 the results were far fromsatisfactory. This demonstrated that the slight angle to which thesanding head is displaced from true squareness in the second station ofthe Nylund patent is of no consequence in eliminating the objectionwhich gave rise to the discovery upon which the present invention ispredicated.

In the aforesaid parent application, Ser. No. 860,860 it was observedthat Increasing the angle produces some slight improvement, but notenough to warrant going far beyond the indicated 15. It has now beendiscovered that, if that angle is substantially greater than 15 and thesanding belts are continuously shifted back and forth along the contactdrums for a total edgewise travel of as much as 6 inches at a frequencyof 20 to 30 times per minute, not only is the objectionable grain reliefeliminated, but the heretofore unheard of feed rate of 800 feet perminute becomes standard operating procedure.

Moreover, from experience with a prototype machine built in accordancewith this invention, it was found that the sanding belts did not requirecleaning nearly as often as heretofore and that the useful life of thebelts was significantly extended. To illustrate, prior to this inventionit was customary to clean the abrasive belts at least every 8 hourswhile the belts that were run on the prototype machine built to test theimproved version of this invention did not require cleaning oftener thanevery 16 hours, and that after 40 hours of use, the belts were stillgood.

With these observations and objectives in mind, the manner in which theinvention achieves its purpose will be appreciated from the followingdescription and the accompanying drawings, which exemplify theinvention, it being understood that such changes in the specificapparatus disclosed herein may be made as come within the scope of theappended claims.

The accompanying drawings illustrate several complete examples of theembodiments of the invention constructed according to the best mode sofar devised for the practical appli cation of the principles thereof,and in which:

FIG. 1 is a combination side view and vertical section through a sandingmachine and its work feeding conveyor, more or less diagrammaticallyillustrated and equipped with one embodiment of the invention;

FIG. 2 is a top view of the machine shown in FIG. 1;

FIG. 3 is a view similar to FIG. 2 but illustrating another way ofcarrying this invention into effect;

FIG. 4 is a view very similar to FIG. 3 but depicting the improvedversion of this invention; and

FIG. 5 is a vertical sectional view through the machine, substantiallyon the plane of the line 5-5 in FIG. 4, but showing only the upper halfof the machine.

Referring to the drawings, and considering first that embodiment of theinvention illustrated in FIGS. 1 and 2, the numeral 5 designatesgenerally a sanding machine of the type disclosed in the aforesaidNylund patent, and which comprises an upper unit 6 and a lower unit 7.Each unit has a sanding head 8 which includes an endless abrasive belt 9trained about at least two rolls l0 and 11, the latter being a contactdrum in that it holds the abrasive belt against the workpiece fedthrough the machine. One of the rolls, preferably the contact drum ispower driven to cause the belt to travel at high speed and repeatedlybring the entire length of the belt into sanding engagement with thework. The belt travels at a speed of over six-thousand surface feet perminute (6000 sfpm) and in the direction opposite the direction in whichthe work moves through the machine.

The contact drums of the two sanding heads are directly one above theother with their axes parallel, and since the sanding heads are fixedwith respect to their respective units 6 and 7, and the support thecontact drums give the belt running over them is unyielding, thedistance between the superimposed units 6 and 7 determines the amountremoved from each side of the workpieces passed through the machine andbetween the complementary upper and lower sanding heads.

Hydraulic rams 12 adjustably support the upper unit 6 from the lowerunit 7 and enable adjustment of the machine to different sized stock;and also provide for the adjustment of the depth of the cut to be madeby each sanding head.

To feed the work through the machine, cooperating sets of power drivenupper and lower feed rollers l3, 13' are provided. These rollers usuallyhave rubber treads and may be spring loaded to have and maintain goodtractive engagement with the workpieces they feed through the machine.All of these feed rollers move the work along the same straight pathnormal or perpendicular to the axes of the contact drums and midwaybetween their adjacent surfaces. Hence the narrow zones of workperforming engagement between the abrasive belts and the opposite sidesof the workpieces moving through the machine are at right angles to ordirectly crosswise of the path along which the workpieces are conveyed.

The workpieces are fed into the machine by a conveyor 14 which maycomprise an endless belt 15 trained over horizontally spaced rolls 16,17 that are joumalled in bearings mounted on a frame 18. The frame is ofsuch height that the upper stretch of the conveyor belt is level withthe entrance into the sanding machine, and the adjacent roll 16 isdriven through a variable speed drive unit 19 so that workpieces placedupon the conveyor belt will be advanced into the machine at a speedcommensurate with the desired feed rate of the machine for instance, 150fpm in the embodiment of the invention shown in FIGS. 1 and 2.

Suitably fixed to the frame 17 and disposed above the upper stretch ofthe conveyor belt is a guide fence 20. This fence is at an angle of 15to the path of the conveyor belt and workpieces placed thereon. Thuswhen the workpieces as, for instance, the four boards B shown in FIG. 2are placed on the conveyor belt and collectively pressed against thefence, they will be properly oriented for passage through the machine.

A gate 21 extends across the conveyor belt near its delivery end torestrain the workpieces placed on the belt until they are properlypositioned as determined by the guide fence; and then the gate islifted, as by hydraulic or pneumatic cylinders 22. In this manner, allof the boards B will move into the machine at the correct angle of 15 tothe path of their travel, so that when they pass between the sandingbelts the narrow zones of work performing engagement between the beltsand the opposite sides of the boards will be oblique to the longitudinaledges of the boards by an angle of 75, with the result that the sandingwill be partially cross grain.

The same result is obtained, if as in FIG. 3 the sanding heads, andespecially the contact drums thereof, are displaced 15 from theirconventional positions. In this case the guide fence is of courseomitted and the workpieces are fed straight through the machine with thegrain parallel to the path of the conveyor.

As will be readily appreciated, in the two embodiments of the inventionillustrated in FIGS. 1 and 2 and 3 the conveyor means by which theworkpieces are fed to and through the machine consists of the feedrollers 13, 13', and the conveyor 14; and while the greatest advantageof the invention no doubt rests with sanding machines of the typedescribed, wherein both sides of the workpieces are simultaneouslysanded, the invention will also improve the results obtained with themore conventional sanding machines in which only one side is sanded.

In the improved version of the invention illustrated in FIGS. 4 and 5,the machine is essentially the same as the one shown in FIG. 3.Accordingly, it has upper and lower sanding units each of whichcomprises superimposed rolls with an abrasive belt 9 trained thereover.In each case, one of the superimposed rolls is the contact drum 11', andthe other the idler roll 10. Since FIG. 4 is a top view of the machine,only the idler roll 10 of the upper sanding unit is visible, but in FIG.5 both rolls are shown.

As seen in FIG. 5, which illustrates only the upper sanding unit and,for clarity, omits some structural details, the contact drum 11 isjournaled in bearings 24 fixedly suspended from the underside of a beam25 that is a rigid part of the frame of the machine. The idler roll 10is journaled in bearings 26 on a yoke 27 that is mounted on the beam 25for limited up and down belt-tensioning adjustment, and for oscillationabout a vertical axis that intersects the axes of the contact drum andthe idler roll medially of the ends thereof.

Belt tensioning adjustment of the yoke 27 is effected conventionally bymeans of a pneumatic cylinder 28 that is coaxial with the axis aboutwhich the yoke and the idler roll oscillate.

Oscillation is imparted to the yoke 27 by a motor 29 that producesconstant reciprocation. Preferably, the motor 29 is a pneumatic cylinderfixed to the beam 25, with its piston connected to an arm 30 thatextends downwardly from the yoke. The angle through which the idler rollis oscillated (indicated in dotted lines in FIG. 4) extends far enoughto either side of parallelism with the contact drum to cause the sandingbelt to shift or travel edgewise along the contact drum a substantialdistance. Experience has shown that a total edgewise travel of at least6 inches produces good results, and that the frequency of theoscillations should be between 20 and 30 per minute.

Control of the motor 29 to effect reversal thereof can be accomplishedin any desired way, as for instance in the manner it is done in US. Pat.No. 3,1 18,314, where the oscillation of the idler roll was employedprimarily to control tracking of the belt.

Although the width of the sanding belt is a matter of choice and limitedonly by factors that control the overall size of the machine, a beltwidth of at least 18 inches is desirable which, of course, means thatthe contact drum and idler roll must be at least 25 or 26 inches long.The distance the belt is shifted back and forth along the contact drumbears a relationship to the width of the belt and should beapproximately one-third that dimension.

The grit size of the abrasive belt is also a matter of choice,

, but for sizing rough sawn lumber that has been cut to dimensionsslightly more than 0.050 of an inch greater than the desired size, agrit size between 24 and 60 produces good results.

As in the embodiment of the invention shown in FIG. 3, the contact drums11' extend obliquely across the path of the lumber or other work passedthrough the machine, but as noted hereinbefore the degree of obliquenessis greater in the improved version of the invention. For best results,the angle at which the contact drums are disposed should be at least 20less than the ninety degrees of conventional sanding machines. A greaterdivergence from squareness is even better, but design considerationsmake it impracticable to exceed an angle of 30. Below 20, the resultsobtained are noticeably inferior but still acceptable at the 15identified in the aforesaid parent application. Hence, the angle atwhich the contact drums are set should be between 15 and 30 less thansquareness with the path of the work, and preferably at least 20. Thismeans that the narrow zone of work performing engagement between theabrasive belts and the top and bottom of the lumber or other work movingthrough the machine, extends obliquely across its path at an angle ofbetween 60 and 75, and preferably not more than 75.

For the contact drums to extend obliquely across the path of the work,the beams 25 and also the idler rolls must be similarly disposed.

Obviously, of course, for the lumber or other work to be fed through themachine at the high rate of 800 feet per minute, the feed rolls of themachine must grip the same tightly and feed the work with a force thatexceeds the opposing force exerted upon the lumber or other work by theoppositely travelling abrasive belts.

Those skilled in the art will also appreciate that the invention can beembodied in forms other than as herein disclosed for purposes ofillustration.

The invention is defined by the following claims:

1. The method of sanding a flat wooden surface of a workpiece whereinthe grain at said surface runs lengthwise of the workpiece, whichcomprises:

A. training an endless fast moving abrasive belt over a plurality ofrolls, one of which is a contact drum;

B. feeding the workpiece along a straight path transverse to the axis ofthe contact drum with the abrasive belt pressed by the contact drumagainst the surface to be sanded along a narrow work performing zonethat is parallel to the axis of the contact drum and transverse to thedirection of the grain at said workpiece surface; and

C. so constraining the path of the workpiece with respect to the axis ofthe contact drum that said narrow zone of work performing engagementbetween the abrasive belt and said workpiece surface is maintained at anoblique angle of substantially no more than 75 to the longitudinaldimension of the workpiece.

2. The method of sanding a flat wooden surface of a workpiece whereinthe grain at said surface runs lengthwise of the workpiece, whichcomprises:

A. training an endless fast moving abrasive belt over a plurality ofrolls, one of which is a contact drum;

B. feeding the workpiece along a straight path transverse to the axis ofthe contact drum with the abrasive belt pressed by the contact drumagainst the surface to be sanded along a narrow work performing zonethat is parallel to the axis of the contact drum and transverse to thedirection of the grain at said workpiece surface; and

C. so relating the axis of the contact drum with respect to the path ofthe workpiece that said narrow zone of work performing engagementbetween the abrasive belt and said workpiece surface forms an obliqueangle of between 60 and 75 to the path of the workpiece.

3. The method of claim 2, wherein said oblique angle is not greater than75.

4. The method of claim 3, further characterized in continually shiftingthe abrasive belt edgewise back and forth along the contact drum.

5. The method of claim 4, wherein the distance through which theabrasive belt is shifted is substantial.

6. The method of claim 5, wherein the distance through which theabrasive belt is shifted is approximately one-third the width of thebelt.

7. The method of claim 6, further characterized in that the rate atwhich the workpiece is fed past the contact drum is approximately 800feet per minute. I

8. The method of claim 6, wherein the frequency at which the belt isshifted back and forth is between 20 and 30 per minute.

1. The method of sanding a flat wooden surface of a workpiece whereinthe grain at said surface runs lengthwise of the workpiece, whichcomprises: A. training an endless fast moving abrasive belt over aplurality of rolls, one of which is a contact drum; B. feeding theworkpiece along a straight path transverse to the axis of the contactdrum with the abrasive belt pressed by the contact drum against thesurface to be sanded along a narrow work performing zone that isparallel to the axis of the contact drum and transverse to the directionof the grain at said workpiece surface; and C. so constraining the pathof the workpiece with respect to the axis of the contact drum that saidnarrow zone of work performing engagement between the abrasive belt andsaid workpiece surface is maintained at an oblique angle ofsubstantially no more than 75* to the longitudinal dimension of theworkpiece.
 2. The method of sanding a flat wooden surface of a workpiecewherein the grain at said surface runs lengthwise of the workpiece,which comprises: A. training an endless fast moving abrasive belt over aplurality of rolls, one of which is a contact drum; B. feeding theworkpiece along a straight path transverse to the axis of the contactdrum with the abrasive belt pressed by the contact drum against thesurface to be sanded along a narrow work performing zone that isparallel to the axis of the contact drum and transverse to the directionof the grain at said workpiece surface; and C. so relating the axis ofthe contact drum with respect to the path of the workpiece that saidnarrow zone of work performing engagement between the abrasive belt andsaid workpiece surface forms an oblique angle of between 60* and 75* tothe path of the workpiece.
 3. The method of claim 2, wherein saidoblique angle is not greater than 75*.
 4. The method of claim 3, furthercharacterized in continually shifting the abrasive belt edgewise backand forth along the contact drum.
 5. The method of claim 4, wherein thedistance through which the abrasive belt is shifted is substantial. 6.The method of claim 5, wherein the distance through which the abrasivebelt is shifted is approximately one-third the width of the belt.
 7. Themethod of claim 6, further characterized in that the rate at which theworkpiece is fed past the contact drum is approximately 800 feet perminute.
 8. The method of claim 6, wherein the frequency at which thebelt is shifted back and forth is between 20 and 30 per minute.